The present invention relates to gas turbine engines and, more particularly, to high energy particle arrestors that are placed in starter turbines to inhibit damage to surrounding equipment in the event of an internal mechanical failure within the turbine housing.
Many relatively large turbine engines, including turbofan jet engines, may use an air turbine starter (ATS) to initiate their rotation. The ATS is mounted by the jet engine, much as a starter for an automobile is located by the automobile""s engine. The ATS may be coupled to a high pressure fluid source, such as compressed air, which impinges upon the turbine wheel in the ATS causing it to rotate at a relatively high rate of speed. The ATS includes an output shaft that is coupled, perhaps via one or more gears, to the jet engine. The output shaft rotation in turn causes the jet engine to begin rotating. The applicant for the present invention, Honeywell International, Inc., has for years successfully designed, developed and manufactured ATSs.
Air turbine starters are robustly manufactured and operationally safe. Nonetheless, for conservatism and/or to meet certain regulatory requirements, ATSs may be analyzed for certain postulated failure modes, that may occur under certain, highly unlikely conditions. For example, one particular type of postulated failure mode that ATSs may be analyzed for is a turbine wheel failure. A turbine wheel failure may be caused by a postulated failure of the turbine wheel itself, including the turbine wheel hub, the turbine wheel blades, or both, or by failure of the thrust bearing assembly that rotationally mounts the turbine wheel. No matter the specific postulated failure mode, if a turbine wheel failure occurs at a relatively high rotational speed (e.g., several thousand r.p.m.), high energy fragments or particles can be expelled from the ATS housing and may cause damage to surrounding components and structure, including the large turbine engine.
To inhibit relatively high energy fragments from penetrating the ATS housing and causing collateral damage, many ATSs include a containment ring. The containment ring may be made of relatively high strength material and is positioned radially outward from the turbine wheel. Some ATSs may also include a cutter ring positioned proximate the turbine wheel hub. The cutter ring is operable to sever the turbine blades if the thrust bearing fails.
Although the above-described containment mechanisms may inhibit a majority of fragments from penetrating the ATS housing, some smaller, relatively high energy particles may still exit the ATS through the ATS""s fluid exhaust passage. To inhibit the egress of these particles at high energy, an ATS may include a plurality of flat disks that are mounted to the ATS housing, and positioned over the exhaust outlet port. However, these disks inhibit only a fraction of the particles that may be ejected from the exhaust passage. Thus, collateral damage can still occur. One reason for this is that the disks, due to their structure and location, may not block particles that originate in the line of sight of the exhaust outlet port. Another weakness of these disks is their shape, which makes them conducive to vibration induced fatigue. Moreover, because the disks are mounted to the ATS housing, the size envelope of the ATS increases.
Hence, there is a need for a particle arrestor that substantially inhibits high energy particles from exiting a turbine housing. There is additionally a need for a particle arrestor that is less conducive to vibration induced fatigue failure. There is also a need for a particle arrestor that, when installed, does not increase the turbine""s size envelope. The present invention addresses these needs.
The present invention provides a particle arrestor for a gas turbine that substantially inhibits relatively high energy particles from exiting the gas turbine housing, thus substantially inhibiting collateral damage to surrounding equipment and structure, and/or that is less conducive to vibration induced fatigue failure, and/or does not increase the starter turbine""s size envelope.
In one aspect of the present invention, a gas turbine includes a turbine housing, a turbine wheel, and at least one particle arrestor ring. The turbine housing has an annular fluid flow passage extending through it that extends from a fluid inlet port through a substantially axial flow portion and then through a substantially curved radial flow portion to a fluid outlet port. The turbine wheel is rotationally mounted within the turbine housing and has at least two turbine blades extending radially into the axial flow portion. The particle arrestor ring has an inner peripheral portion and an outer peripheral portion, and is mounted within the curved radial flow portion such that the inner peripheral portion is positioned proximate the turbine blades.
In another aspect of the invention, a particle arrestor ring is provided for insertion into a gas turbine engine having an annular fluid flow passage extending from a fluid inlet port through a substantially axial flow portion and then through a substantially curved radial flow portion to a fluid outlet port, and having a turbine wheel rotationally mounted within the turbine housing and having at least two turbine blades extending radially into the axial flow portion. The particle arrestor ring includes a main body portion bounded by an inner peripheral portion and an outer peripheral portion, the main body portion has a generally conical shape, and has a substantially curved cross section extending between the inner peripheral portion and the outer peripheral portion.
In yet another aspect of the present invention, in a gas turbine engine having an annular fluid flow passage extending from a fluid inlet port through a substantially axial flow portion and then through a substantially curved radial flow portion to a fluid outlet port, and having a turbine wheel rotationally mounted within the turbine housing and having at least two turbine blades extending radially into the axial flow portion, a method of modifying the turbine to include at least one particle arrestor ring having a main body portion bounded by an inner peripheral portion and an outer peripheral portion includes the step of disassembling at least a portion of the housing. Then, at least one particle arrestor ring is inserted into the radial flow portion, and mounting each particle arrestor ring in the turbines radial flow portion such that its inner peripheral portion is positioned proximate the turbine blades.
Other independent features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.